Current File : //backups/router/usr/include/sys/buf_ring.h
/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* Copyright (c) 2007-2009 Kip Macy <kmacy@freebsd.org>
* All rights reserved.
* Copyright (c) 2024 Arm Ltd
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
*/
#ifndef _SYS_BUF_RING_H_
#define _SYS_BUF_RING_H_
#include <sys/param.h>
#include <sys/kassert.h>
#include <machine/atomic.h>
#include <machine/cpu.h>
#if defined(DEBUG_BUFRING) && defined(_KERNEL)
#include <sys/lock.h>
#include <sys/mutex.h>
#endif
/*
* We only apply the mask to the head and tail values when calculating the
* index into br_ring to access. This means the upper bits can be used as
* epoch to reduce the chance the atomic_cmpset succeedes when it should
* fail, e.g. when the head wraps while the CPU is in an interrupt. This
* is a probablistic fix as there is still a very unlikely chance the
* value wraps back to the expected value.
*
*/
struct buf_ring {
volatile uint32_t br_prod_head;
volatile uint32_t br_prod_tail;
int br_prod_size;
int br_prod_mask;
uint64_t br_drops;
volatile uint32_t br_cons_head __aligned(CACHE_LINE_SIZE);
volatile uint32_t br_cons_tail;
int br_cons_size;
int br_cons_mask;
#if defined(DEBUG_BUFRING) && defined(_KERNEL)
struct mtx *br_lock;
#endif
void *br_ring[0] __aligned(CACHE_LINE_SIZE);
};
/*
* multi-producer safe lock-free ring buffer enqueue
*
*/
static __inline int
buf_ring_enqueue(struct buf_ring *br, void *buf)
{
uint32_t prod_head, prod_next, prod_idx;
uint32_t cons_tail, mask;
mask = br->br_prod_mask;
#ifdef DEBUG_BUFRING
/*
* Note: It is possible to encounter an mbuf that was removed
* via drbr_peek(), and then re-added via drbr_putback() and
* trigger a spurious panic.
*/
for (uint32_t i = br->br_cons_head; i != br->br_prod_head; i++)
if (br->br_ring[i & mask] == buf)
panic("buf=%p already enqueue at %d prod=%d cons=%d",
buf, i, br->br_prod_tail, br->br_cons_tail);
#endif
critical_enter();
do {
/*
* br->br_prod_head needs to be read before br->br_cons_tail.
* If not then we could perform the dequeue and enqueue
* between reading br_cons_tail and reading br_prod_head. This
* could give us values where br_cons_head == br_prod_tail
* (after masking).
*
* To work around this us a load acquire. This is just to
* ensure ordering within this thread.
*/
prod_head = atomic_load_acq_32(&br->br_prod_head);
prod_next = prod_head + 1;
cons_tail = atomic_load_acq_32(&br->br_cons_tail);
if ((int32_t)(cons_tail + br->br_prod_size - prod_next) < 1) {
rmb();
if (prod_head == br->br_prod_head &&
cons_tail == br->br_cons_tail) {
br->br_drops++;
critical_exit();
return (ENOBUFS);
}
continue;
}
} while (!atomic_cmpset_acq_32(&br->br_prod_head, prod_head, prod_next));
prod_idx = prod_head & mask;
#ifdef DEBUG_BUFRING
if (br->br_ring[prod_idx] != NULL)
panic("dangling value in enqueue");
#endif
br->br_ring[prod_idx] = buf;
/*
* If there are other enqueues in progress
* that preceded us, we need to wait for them
* to complete
*/
while (br->br_prod_tail != prod_head)
cpu_spinwait();
atomic_store_rel_32(&br->br_prod_tail, prod_next);
critical_exit();
return (0);
}
/*
* multi-consumer safe dequeue
*
*/
static __inline void *
buf_ring_dequeue_mc(struct buf_ring *br)
{
uint32_t cons_head, cons_next, cons_idx;
uint32_t prod_tail, mask;
void *buf;
critical_enter();
mask = br->br_cons_mask;
do {
/*
* As with buf_ring_enqueue ensure we read the head before
* the tail. If we read them in the wrong order we may
* think the bug_ring is full when it is empty.
*/
cons_head = atomic_load_acq_32(&br->br_cons_head);
cons_next = cons_head + 1;
prod_tail = atomic_load_acq_32(&br->br_prod_tail);
if (cons_head == prod_tail) {
critical_exit();
return (NULL);
}
} while (!atomic_cmpset_acq_32(&br->br_cons_head, cons_head, cons_next));
cons_idx = cons_head & mask;
buf = br->br_ring[cons_idx];
#ifdef DEBUG_BUFRING
br->br_ring[cons_idx] = NULL;
#endif
/*
* If there are other dequeues in progress
* that preceded us, we need to wait for them
* to complete
*/
while (br->br_cons_tail != cons_head)
cpu_spinwait();
atomic_store_rel_32(&br->br_cons_tail, cons_next);
critical_exit();
return (buf);
}
/*
* single-consumer dequeue
* use where dequeue is protected by a lock
* e.g. a network driver's tx queue lock
*/
static __inline void *
buf_ring_dequeue_sc(struct buf_ring *br)
{
uint32_t cons_head, cons_next, cons_idx;
uint32_t prod_tail, mask;
void *buf;
mask = br->br_cons_mask;
cons_head = br->br_cons_head;
prod_tail = atomic_load_acq_32(&br->br_prod_tail);
cons_next = cons_head + 1;
if (cons_head == prod_tail)
return (NULL);
cons_idx = cons_head & mask;
br->br_cons_head = cons_next;
buf = br->br_ring[cons_idx];
#ifdef DEBUG_BUFRING
br->br_ring[cons_idx] = NULL;
#ifdef _KERNEL
if (!mtx_owned(br->br_lock))
panic("lock not held on single consumer dequeue");
#endif
if (br->br_cons_tail != cons_head)
panic("inconsistent list cons_tail=%d cons_head=%d",
br->br_cons_tail, cons_head);
#endif
atomic_store_rel_32(&br->br_cons_tail, cons_next);
return (buf);
}
/*
* single-consumer advance after a peek
* use where it is protected by a lock
* e.g. a network driver's tx queue lock
*/
static __inline void
buf_ring_advance_sc(struct buf_ring *br)
{
uint32_t cons_head, cons_next, prod_tail;
#ifdef DEBUG_BUFRING
uint32_t mask;
mask = br->br_cons_mask;
#endif
cons_head = br->br_cons_head;
prod_tail = br->br_prod_tail;
cons_next = cons_head + 1;
if (cons_head == prod_tail)
return;
br->br_cons_head = cons_next;
#ifdef DEBUG_BUFRING
br->br_ring[cons_head & mask] = NULL;
#endif
atomic_store_rel_32(&br->br_cons_tail, cons_next);
}
/*
* Used to return a buffer (most likely already there)
* to the top of the ring. The caller should *not*
* have used any dequeue to pull it out of the ring
* but instead should have used the peek() function.
* This is normally used where the transmit queue
* of a driver is full, and an mbuf must be returned.
* Most likely whats in the ring-buffer is what
* is being put back (since it was not removed), but
* sometimes the lower transmit function may have
* done a pullup or other function that will have
* changed it. As an optimization we always put it
* back (since jhb says the store is probably cheaper),
* if we have to do a multi-queue version we will need
* the compare and an atomic.
*/
static __inline void
buf_ring_putback_sc(struct buf_ring *br, void *new)
{
uint32_t mask;
mask = br->br_cons_mask;
KASSERT((br->br_cons_head & mask) != (br->br_prod_tail & mask),
("Buf-Ring has none in putback")) ;
br->br_ring[br->br_cons_head & mask] = new;
}
/*
* return a pointer to the first entry in the ring
* without modifying it, or NULL if the ring is empty
* race-prone if not protected by a lock
*/
static __inline void *
buf_ring_peek(struct buf_ring *br)
{
uint32_t cons_head, prod_tail, mask;
#if defined(DEBUG_BUFRING) && defined(_KERNEL)
if ((br->br_lock != NULL) && !mtx_owned(br->br_lock))
panic("lock not held on single consumer dequeue");
#endif
mask = br->br_cons_mask;
prod_tail = atomic_load_acq_32(&br->br_prod_tail);
cons_head = br->br_cons_head;
if (cons_head == prod_tail)
return (NULL);
return (br->br_ring[cons_head & mask]);
}
static __inline void *
buf_ring_peek_clear_sc(struct buf_ring *br)
{
uint32_t cons_head, prod_tail, mask;
void *ret;
#if defined(DEBUG_BUFRING) && defined(_KERNEL)
if (!mtx_owned(br->br_lock))
panic("lock not held on single consumer dequeue");
#endif
mask = br->br_cons_mask;
prod_tail = atomic_load_acq_32(&br->br_prod_tail);
cons_head = br->br_cons_head;
if (cons_head == prod_tail)
return (NULL);
ret = br->br_ring[cons_head & mask];
#ifdef DEBUG_BUFRING
/*
* Single consumer, i.e. cons_head will not move while we are
* running, so atomic_swap_ptr() is not necessary here.
*/
br->br_ring[cons_head & mask] = NULL;
#endif
return (ret);
}
static __inline int
buf_ring_full(struct buf_ring *br)
{
return (br->br_prod_head == br->br_cons_tail + br->br_cons_size - 1);
}
static __inline int
buf_ring_empty(struct buf_ring *br)
{
return (br->br_cons_head == br->br_prod_tail);
}
static __inline int
buf_ring_count(struct buf_ring *br)
{
return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail)
& br->br_prod_mask);
}
#ifdef _KERNEL
struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags,
struct mtx *);
void buf_ring_free(struct buf_ring *br, struct malloc_type *type);
#else
#include <stdlib.h>
static inline struct buf_ring *
buf_ring_alloc(int count)
{
struct buf_ring *br;
KASSERT(powerof2(count), ("buf ring must be size power of 2"));
br = calloc(1, sizeof(struct buf_ring) + count * sizeof(void *));
if (br == NULL)
return (NULL);
br->br_prod_size = br->br_cons_size = count;
br->br_prod_mask = br->br_cons_mask = count - 1;
br->br_prod_head = br->br_cons_head = 0;
br->br_prod_tail = br->br_cons_tail = 0;
return (br);
}
static inline void
buf_ring_free(struct buf_ring *br)
{
free(br);
}
#endif /* !_KERNEL */
#endif /* _SYS_BUF_RING_H_ */
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